Griseofulvin
Also known as: Fulvicin · AmTech Griseofulvin · Grifulvin V · Gris-PEG · Curling factor · Griseofulvina · Griseofulvinum
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible dermatophytic infections | Microsize: 25 mg/kg q12h PO for 42-56 days; Ultramicrosize: 5-10 mg/kg PO once daily for 42 days. | PO | q12h or once daily | 42-56 days | 🌎 NA |
| Susceptible dermatophytic infections | Microsize: 50 mg/kg PO once daily with fatty meal. | PO | once daily | Prolonged | 🌎 NA |
- Susceptible dermatophytic infections: May need to treat longer for Trichophyton than for Microsporum. Give following a fatty meal or administration of corn oil. Continue for at least 2 weeks after resolution of signs and at least 5 months for onychomycosis.
- Susceptible dermatophytic infections: Used with topical therapy. May double dose in resistant cases. If GI distress occurs may divide dose and give twice daily with food. Begin taking cultures after 4 weeks. Continue therapy for 2 weeks beyond clinical cure and when 2-3 negative cultures are obtained at weekly intervals.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible dermatophytic infections | Microsize: 50-120 mg/kg PO; divided daily. Ultramicrosize: 10-15 mg/kg PO twice daily. | PO | divided daily or twice daily | 4-6 weeks or longer | 🌎 NA |
| Susceptible dermatophytic infections | Microsize: 50 mg/kg PO once daily or 25 mg/kg PO q12h for 42-70 days; Ultramicrosize: 5-10 mg/kg PO once daily for 42 days. | PO | once daily or q12h | 42-70 days | 🌎 NA |
| Susceptible dermatophytic infections | Microsize: 50 mg/kg PO once daily with fatty meal. | PO | once daily | Prolonged | 🌎 NA |
| Feline eosinophilic granuloma complex | Microsize: 25 mg/kg PO twice daily with food. | PO | twice daily | At least one month | 🌎 NA |
- Susceptible dermatophytic infections: Give with a fatty meal. Treat until culture is negative.
- Susceptible dermatophytic infections: Give following a fatty meal or administration of corn oil. Continue for at least 2 weeks after resolution of signs and at least 5 months for onychomycosis.
- Susceptible dermatophytic infections: Used with topical therapy. May double dose in resistant cases. If GI distress occurs may divide dose and give twice daily with food. Begin taking cultures after 4 weeks. Continue therapy for 2 weeks beyond clinical cure and when 2-3 negative cultures are obtained at weekly intervals.
- Feline eosinophilic granuloma complex: Give at least for one month to judge efficacy.
Small Mammals
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Advanced dermatophytosis (Rabbits) | Ultramicrosize 6.25 mg/kg PO q12h for 4-6 weeks. Microsize: 25 mg/kg PO q12-24h for one month | PO | q12h or q12-24h | 4-6 weeks or 1 month | 🌎 NA |
| Susceptible dermatophytic infections (Chinchillas) | 25 mg/kg PO once daily for 30-60 days | PO | once daily | 30-60 days | 🌎 NA |
| Susceptible dermatophytic infections (Gerbils, Guinea pigs, Hamsters, Rats) | 25 mg/kg PO q24h for 14-28 days | PO | q24h | 14-28 days | 🌎 NA |
| Susceptible dermatophytic infections (Mice) | 25 mg/kg PO q24h for 14 days | PO | q24h | 14 days | 🌎 NA |
| Susceptible dermatophytic infections (Chinchillas) | 25 mg/kg PO q24h for 28-40 days | PO | q24h | 28-40 days | 🌎 NA |
| Dermatophytosis (Guinea pigs) | 25 mg/kg PO (as a suspension) once daily for 28 days. | PO | once daily | 28 days | 🌎 NA |
| Susceptible dermatophytic infections (Chinchillas) | 25 mg/kg PO once daily (q24h) for 30 days | PO | once daily | 30 days | 🌎 NA |
Birds
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible dermatophytic infections (Ratites) | 35-50 mg/kg PO once daily | PO | once daily | — | 🌎 NA |
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible dermatophytic infections | Using the microsize (not ultra-microsize) products: 5 mg/kg PO once daily. | PO | once daily | — | 🌎 NA |
- Susceptible dermatophytic infections: Smaller doses (1.25 grams) should be used for foals or ponies. If using ultra-microsize (human) formulations the dose should be reduced by 50%.
Cattle
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible dermatophytic infections | Ultramicrosize: 10-20 mg/kg PO once daily for 1-2 weeks. 100 mg/kg PO given twice (or more) 1 week apart may also be effective. | PO | once daily or weekly | 1-2 weeks | 🌎 NA |
| Susceptible dermatophytic infections | 20 mg/kg PO once daily for 6 weeks | PO | once daily | 6 weeks | 🌎 NA |
- Susceptible dermatophytic infections: Not FDA-approved for use in food animals and can be very expensive.
Swine
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible dermatophytic infections | 20 mg/kg PO once daily for 6 weeks | PO | once daily | 6 weeks | 🌎 NA |
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Griseofulvin is a fungistatic antibiotic used primarily in veterinary medicine to treat dermatophytic fungal infections (ringworm) of the skin, hair, and claws.
Key Clinical Points:
- It is highly specific to dermatophytes (e.g., Trichophyton, Microsporum, and Epidermophyton).
- It has no efficacy against bacteria, other pathogenic fungi, or Malassezia yeasts.
- Clinical Pearl: Due to its potential for significant adverse effects (especially bone marrow suppression and teratogenicity) and the need for prolonged therapy, griseofulvin is increasingly being replaced in modern veterinary practice by newer, safer antifungals such as itraconazole and terbinafine.
- Dosing differs significantly between the microsize and ultramicrosize formulations due to differences in gastrointestinal absorption.
Mechanism of action
Griseofulvin is a fungistatic agent. It enters susceptible fungal cells and binds to tubulin, which disrupts the structure of the mitotic spindle → arresting the metaphase of cell division.
Additionally, griseofulvin binds to newly synthesized keratin in the host. As new skin, hair, and nails grow, the keratin-griseofulvin complex makes these newly formed tissues resistant to fungal invasion, allowing the infected, older tissues to be shed.
Safety & warnings
Contraindications
- Pregnancy (known teratogen)
- Known hypersensitivity to griseofulvin
- Hepatocellular failure
- Horses intended for food
Adverse effects
- Anorexia
- Vomiting
- Diarrhea
- Anemia
- Neutropenia
- Leukopenia
- Thrombocytopenia
- Depression
- Ataxia
- Hepatotoxicity
- Dermatitis/photosensitivity
- Toxic epidermal necrolysis
- Teratogenesis
Precautions
Important Warnings:
- Feline Sensitivity: Cats, particularly kittens, are highly susceptible to adverse effects (e.g., bone marrow depression), likely due to slower glucuronide conjugation. Monitor carefully.
- FIV Testing: Cats should be tested for FIV before initiating therapy due to the drug's potential neutropenic or panleukopenic effects.
- Teratogenicity: Griseofulvin is a known teratogen (causes cleft palate, skeletal/brain malformations). It is strictly contraindicated in pregnant animals. It may also inhibit spermatogenesis.
- Absorption: Must be given with a fatty meal to ensure adequate GI absorption.
Drug interactions
Griseofulvin may potentiate the effects of alcohol.
Griseofulvin may decrease salicylate levels.
Griseofulvin may decrease cyclosporine levels.
May decrease griseofulvin blood concentrations by inducing hepatic microsomal enzymes and/or reducing absorption. Dosage adjustment may be necessary.
May decrease theophylline half-life and levels in some patients.
May reduce the anticoagulant activity of coumarin anticoagulants; adjustment may be required.
Monitoring
- Clinical efficacy; fungal culture
- Adverse effects
- CBC; before therapy and q1-3 weeks during therapy
- Liver enzymes (if indicated)
Pharmacokinetics
Half-life
Absorption
Microsized form is variably absorbed (25-70%); dietary fat enhances absorption. Ultramicrosize form is nearly 100% absorbed (approximately 1.5 times as well as the microsized form).
Distribution
Concentrates in skin, hair, nails, fat, skeletal muscle, and the liver. Can be found in the stratum corneum within 4 hours of dosing.
Metabolism
Metabolized by the liver via oxidative demethylation and glucuronidation to 6-desmethylgriseofulvin (inactive).
Elimination
Less than 1% of the drug is excreted unchanged in the urine.
Overdose
Specifics regarding acute toxicity are limited. Significant overdoses should be managed with gut emptying, activated charcoal, and cathartic administration unless contraindicated. Horses have tolerated 100 mg/kg PO for 20 days without apparent ill effect.
Available products
Formulations
- Powder
- Oral Tablets
- Oral Suspension
Veterinary
- AmTech® Griseofulvin Powder: 2.5 g griseofulvin in 15 g sachets (FDA-approved for horses not intended for food)
Human-labeled
- Grifulvin V® Griseofulvin Microsize Oral Tablets: 500 mg
- Griseofulvin Microsize Oral Suspension: 125 mg/5 mL
- Gris-PEG® Griseofulvin Ultramicrosize Tablets: 125 mg & 250 mg
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store at less than 40°C, preferably at room temperature (15-30°C). Suspensions should be stored in tight, light-resistant containers. Microsize tablets/capsules should be stored in tight containers; ultramicrosize tablets in well-closed containers.
Client information
Important: Griseofulvin can cause birth defects. Pregnant women should avoid handling this medication, or wear gloves if administration is necessary.
- Administration: Always give this medication with a fatty meal (e.g., a small amount of canned food, butter, or corn oil) to help the body absorb it properly.
- Compliance: Ringworm treatment takes time. Continue giving the medication exactly as prescribed, even if the pet looks better. Stopping too early can cause the infection to return.
- Environmental Control: Ringworm is highly contagious to other pets and humans. Follow your veterinarian's instructions for disinfecting the home, destroying old bedding, and isolating the pet if necessary.
- Side Effects: Watch for loss of appetite, vomiting, or diarrhea. If your pet seems lethargic, uncoordinated, or develops any unusual symptoms, contact your veterinarian immediately.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.